Skip to main content

Research Repository

Advanced Search

Evidence of patchy hydrogen reionization from an extreme Ly? trough below redshift six

Becker, George D.; Bolton, James S.; Madau, Piero; Pettini, Max; Ryan-Weber, Emma V.; Venemans, Bram P.

Evidence of patchy hydrogen reionization from an extreme Ly? trough below redshift six Thumbnail


George D. Becker

Piero Madau

Max Pettini

Emma V. Ryan-Weber

Bram P. Venemans


© 2015 The Authors. We report the discovery of an extremely long (~110 Mpc h -1 ) and dark (τ eff ≳ 7) Lyα trough extending down to z ≃ 5.5 towards the z em ≃ 6.0 quasar ULAS J0148+0600. We use these new data in combination with Lya forest measurements from 42 quasars at 4.5 ≤ z em ≤ 6.4 to conduct an updated analysis of the line-of-sight variance in the intergalactic Lya opacity over 4 ≤ z ≤ 6. We find that the scatter in transmission among lines of sight near z ~ 6 significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near z ≃ 5.6-5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone.We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by z ≃ 5.6, however, a large fraction of the data are consistent with a uniform UVB, and by z ~ 5 the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at z ~ 6, it has fully completed by z ~ 5.


Becker, G. D., Bolton, J. S., Madau, P., Pettini, M., Ryan-Weber, E. V., & Venemans, B. P. (2015). Evidence of patchy hydrogen reionization from an extreme Ly? trough below redshift six. Monthly Notices of the Royal Astronomical Society, 447(4), 3402-3419.

Journal Article Type Article
Acceptance Date Dec 12, 2014
Online Publication Date Jan 22, 2015
Publication Date Mar 11, 2015
Deposit Date Jul 4, 2016
Publicly Available Date Jul 4, 2016
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 447
Issue 4
Pages 3402-3419
Keywords Intergalactic Medium, Quasars, Absorption Lines, Cosmology, Observations, Dark Ages, Reionization, First Stars, Large-scale Structure of the Universe
Public URL
Publisher URL
Additional Information This article has been published in Monthly Notices of the Royal Astronomical Society © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society


3402.full.pdf (1.8 Mb)

Copyright Statement
Copyright information regarding this work can be found at the following address:

You might also like

Downloadable Citations